Kevin Steele, 51, was sentenced to five and a half years imprisonment after he helped fraudster Michael Shephard apply for the multimillion pound loan from a Swiss private bank to develop a luxury hotel resort in Turkey.

The equity partner at Mishcon de Reya, which represented Diana in her divorce from the Prince of Wales, helped Shephard, a client of his, to obtain the £17.5m loan.

The pair used fake documents to back up a bogus claim that Shephard had access to a £76m fortune to secure the loan from the EFG Private Bank, a Swiss-based global company with offices in Mayfair.

Southwark crown court in London heard that they secured the loan by providing forged letters from another private bank to EFG claiming Shephard had the money in offshore accounts.

Prosecutor David Aaronberg QC said: "Mr Shephard was presented as a phenomenally wealthy businessman. He had no money in such bank accounts – the letters were forgeries.

"Mr Shephard was presenting himself as a successful man with these vast sums of money tied up in Swiss bank accounts and he was being supported by Mr Steele."

The court was told that half of the money was used to buy a hotel site in Turkey and the balance of the fraud was put into Shephard's account at the law firm. Steele then used £1.8mn of the money in the account to pay the costs of a Russian client of Mishcon de Reya to whom Steele had given negligent advice, the court was told.

The court was told that Shephard's assistant, Mark Pattinson, who helped create the forged letters, had previously been sentenced.

Steele, of Claygate in Esher, Surrey, was sentenced to five and a half years for conspiracy to commit fraud by false representation, and five and a half years for conspiracy to use false instruments, to run concurrently.

Pattinson, of Preston, Lancashire, and Shephard, of Lancaster, both admitted the charges at an earlier hearing. They were sentenced to 18 months and six years and three months, respectively.

Shephard was also disqualified from being a company director for 15 years.

Steele was also handed a jail term of four years, to run concurrently with the other sentences, for committing fraud by abusing his position at Mischon de Reya between 10 October 2007 and 4 September 2008.